**Question:** Not true about Refsum disease is?

A. Refsum disease is a genetic disorder affecting only children.
B. Refsum disease is caused by a deficiency in vitamin D.
C. Refsum disease is characterized by hearing loss and vision problems.
D. Refsum disease is exclusively associated with neurodegenerative symptoms.

**Core Concept:**
Refsum disease is a rare, inherited disorder that primarily affects the nervous system. It is caused by the deficiency or dysfunction of specific enzymes involved in the breakdown of certain lipids, leading to the accumulation of toxic substances in the body. In this case, the disease is associated with genetic mutations in the PHYH, ALDH4A1, or UGCG genes, which encode for the enzymes involved in the breakdown of biotin-containing fatty acids (phytanic acid) and phytanic acid-related compounds.

**Why the Correct Answer is Right:**
Refsum disease is not true to option A, as it can affect individuals of all ages, not just children. While it is inherited, the genetic mutations can manifest at any age, making this statement incorrect.

**Why Each Wrong Option is Incorrect:**
Option B is incorrect because Refsum disease is primarily caused by a deficiency in the enzyme PCDH17 (phytanic acid 3-dehydrogenase), leading to the accumulation of phytanic acid and related compounds. A deficiency of vitamin D is not the cause of Refsum disease.

Option C is incorrect because Refsum disease affects the nervous system, not just hearing loss and vision problems. Although hearing loss and vision issues are common symptoms, the disease involves multiple organ systems, including the cardiovascular, musculoskeletal, and gastrointestinal systems.

Option D is incorrect because Refsum disease primarily affects the nervous system and can lead to neurodegeneration. While neurodegenerative symptoms are present, the disease does not solely involve neurodegeneration. Refsum disease is a multi-system disorder affecting various organs, including the cardiovascular, musculoskeletal, and gastrointestinal systems.

**Clinical Pearl:**
Refsum disease is an essential example of the importance of considering multiple organ systems in genetic disorders. A thorough clinical examination and understanding of disease manifestations are crucial for accurate diagnosis and appropriate patient management.